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Figure 6 | Biology Direct

Figure 6

From: The Rodin-Ohno hypothesis that two enzyme superfamilies descended from one ancestral gene: an unlikely scenario for the origins of translation that will not be dismissed

Figure 6

Quantitative framework in which to assess the catalytic significance of Urzymes and various other putative stages of aaRS evolution. A. Rate accelerations estimated from experimental data for single substrate (red) and bi-substrate (Black, Bold) reactions adapted from [75] to include uncatalyzed and catalyzed rates of bi-substrate reactions of the ribosome [74], amino acid activation [39] and kinases [106]. Second order rate constants (black bars) were converted into comparable units by multiplying by 0.002 M, which is the ATP concentration used to assay the catalysts shown in B. B. Experimental rate accelerations estimated from steady state kinetics as kcat/KM for a series of catalysts derived from Class I and Class II aminoacyl-tRNA synthetases ([38, 39] and data of V. Weinreb, L. Li, M. Collier, and K. Gonzalez-Rivera presented here in a subsequent section). Vertical scales in A and B are the same, and the origin of the histogram in B has been set equal to the uncatalyzed rate of amino acid activation in (AAact) in A. Red bars denote Class I Tryptophanyl- and Leucyl-tRNA synthetase constructs, blue bars denote Class II Histidyl-tRNA synthetase constructs, and green denotes a ribozymal catalyst [97], included for comparison. Research presented in A, B was originally published in [37]. © The American Society for Biochemistry and Molecular Biology. C. Class I LeuRS and Class II HisRS Urzyme amino acid specificities. Amino acids with more negative ΔGkcat/KM values indicate higher activities. By ~1 kcal/mole (light bands) or ~ five-fold, each Urzyme prefers substrates from the class to which it belongs (dark bands). Nonetheless, both activate a range of non-cognate amino acids, and are promiscuous.

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